Power converters need to detect or reconstruct their output voltage in order to regulate the output voltage to a desired voltage. Power converters need to reconstruct the output voltage and keep it stable for during the switching cycle in order to regulate the output voltage to the desired voltage. Conventional power converters typically reconstruct the output voltage by way of an analog feedback loop using an opto-coupler or a sample-and-hold circuit.
FIG. 1 is a diagram illustrating a conventional power converter that measures the output voltage using an opto-coupler 102. The power converter senses the output voltage Vout via a diode 114 from the secondary winding of the transformer 112. The sensed output voltage Vout is detected on the primary side of the transformer 112 through an opto-coupler 102 which optically couples the output voltage Vout to the primary side but maintains electrical isolation between the secondary side and the primary side of the transformer 112. The coupled signal 103 is passed through a signal-conditioning module 104. The signal-conditioning module 104 is a combination of a filter with a gain stage to generate a usable scaled voltage signal that represents the value of the sensed output voltage Vout, which is the control voltage Vc. The control voltage Vc is compared to a set voltage in an error amplifier 106, and the amplified error signal 107 is input to the gate drive logic 108. The gate drive logic 108 controls when the switch 110 is turned on or off, by generating turn−on timings (tON) and turn−off timings (tOFF) for the switch 110 to regulate the output voltage Vout to the desired voltage.
FIG. 2 is a diagram illustrating a conventional power converter that measures the output voltage using a sample and hold circuit 204. The power converter senses the feedback voltage FB, which is a scaled down version of the output voltage Vout at the secondary winding side of the transformer 214, using an auxiliary winding 220. The feedback voltage FB is sampled from the auxiliary winding 220 at a certain sampling timing. However, because the feedback voltage FB does not remain constant after it is sampled, there is a need for a mechanism to retain the value of the feedback voltage FB until the next sampling timing in order to use the feedback voltage FB to regulate the power converter to a desired voltage. Thus, the feedback voltage FB is input to an amplifier 202 and then through a signal conditioning and sample-and-hold circuit 204 to generate a control voltage Vc. The sample-and-hold circuit 204 holds the value of the feedback voltage FB sampled at the sampling timing at the detected value until the next sampling timing. The held signal 205 is amplified by another amplifier 206 to generate the control voltage Vc. The control voltage Vc is compared to a set voltage in an error amplifier 208, and the amplified error signal output from the error amplifier 208 is input to the gate drive logic 210. The gate drive logic 210 controls when the switch 212 is turned on or off, by generating turn−on timings (tON) and turn−off timings (tOFF) for the switch 212 to regulate the output voltage Vout to the desired voltage.
However, as shown in FIGS. 1 and 2, conventional power converters use additional components such as opto-couplers or sample-and-hold circuits to measure the output voltage of the power converter while isolating the secondary side of the transformer from the primary side of the transformer in the power converter. Using opto-couplers or sample-and-hold circuits have disadvantages. For example, opto-couplers have an inaccurate transfer ratio resulting in error in the measurement, and they are bandwidth-limited. Sample-and-hold circuits have a disadvantage of capacitive leakage, which means that the error in the sample-and-hold circuit becomes greater as the sampling period becomes longer.
Therefore, there is a need for a power converter that can reconstruct its output voltage without using additional components such as opto-couplers or sample-and-hold circuits.